1. Field of the Invention
This invention relates to a thermoplastic resin composition which has a high heat distortion temperature along with excellent impact resistance and moldability.
2. Description of the Prior Art
The methacrylimide group-containing polymer is known as a thermoplastic resin polymer with excellent properties in heat resistance and transparency (U.S. Pat. No. 4,246,374). However, its application as a molding material is considerably restricted due to inferior mechanical properties including impact strength.
Many attempts have been made to eliminate the drawbacks of the methacrylimide group-containing polymer, proposing various methods including, for example, [1] a method of blending acrylonitrile-butadiene-styrene copolymer (ABS resin), methyl methacrylate-butadiene-styrene copolymer (MBS resin) or alkyl acrylate rubber as an impact modifier (Laid-Open Japanese Patent Application 52-63989), [2] a method of blending a butadiene rubber- or alkyl acrylate rubber-base multi-stage polymer in combination with polycarbonate as an impact modifier (Laid-Open Japanese Patent Application 55-80459), and [3] a method of blending a butadiene rubber-base multi-stage polymer in combination with an alkyl acrylate rubber-base multi-stage polymer as an impact modifier.
Nevertheless, the impact strength obtained by the methods [1] and [3] mentioned above are still insufficient. Namely, it is necessary to blend the impact modifier in a large quantity to secure a higher impact strength. This, however, sacrifices the heat resistance inherent to the methacrylimide group-containing polymer as well as its fluidity in molding. On the other hand, the method [2] which intends to improve the impact strength while retaining the molding fluidity fails to produce the intended effects to a sufficient degree because the methacrylimide group-containing polymer has low compatibility with polycarbonate by nature.
For solving these problems, a proposal has been made with regard to an attempt of improving the impact strength by blending the methacrylimide group-containing polymer with a specific thermoplastic elastomer selected from polyether ester, polyether ester amide and polyether amide (Laid-Open Japanese Patent Application 59-49252). Although it is possible to improve the impact strength and molding fluidity by this method, the inherent heat resistance of the methacrylimide group-containing polymer has to be sacrificed to enhance the impact strength further.
Under these circumstances, researches have been conducted with a view to increase the impact strength of the methacrylimide group-containing polymer and to improve the moldability without impairing its inherent heat resistance, and as a result it has been found that these objectives can be attained by blending a specific thermoplastic elastomer and a specific butadiene rubber graft-copolymer with the methacrylimide group-containing polymer.